U.S. patent application number 14/365170 was filed with the patent office on 2014-11-13 for combustion chamber structure for internal combustion engine.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is Kentaro Nishida, Hiroshi Oyagi. Invention is credited to Kentaro Nishida, Hiroshi Oyagi.
Application Number | 20140331957 14/365170 |
Document ID | / |
Family ID | 48612059 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140331957 |
Kind Code |
A1 |
Nishida; Kentaro ; et
al. |
November 13, 2014 |
COMBUSTION CHAMBER STRUCTURE FOR INTERNAL COMBUSTION ENGINE
Abstract
A combustion chamber structure for an internal combustion engine
includes, in a piston top part, a concave portion formed
eccentrically with respect to a cylinder center axis, and a tapered
portion that connects an upper end face of the piston top part and
a side face of the concave portion. The tapered portion is formed
so that a tapered portion volume (volume of a space formed between
the tapered portion and an upper wall surface of the combustion
chamber) in a first portion of the piston top part is greater than
a tapered portion volume in a second portion that is nearer than
the first portion to an eccentric direction of the concave portion
from the cylinder center axis.
Inventors: |
Nishida; Kentaro;
(Susono-shi, JP) ; Oyagi; Hiroshi; (Susono-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Nishida; Kentaro
Oyagi; Hiroshi |
Susono-shi
Susono-shi |
|
JP
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
48612059 |
Appl. No.: |
14/365170 |
Filed: |
December 16, 2011 |
PCT Filed: |
December 16, 2011 |
PCT NO: |
PCT/JP2011/079235 |
371 Date: |
June 13, 2014 |
Current U.S.
Class: |
123/193.1 |
Current CPC
Class: |
F02B 23/0624 20130101;
F02B 23/0693 20130101; F02F 1/00 20130101; F02B 23/0696 20130101;
F02B 23/0621 20130101; F02B 23/069 20130101; Y02T 10/125 20130101;
Y02T 10/12 20130101 |
Class at
Publication: |
123/193.1 |
International
Class: |
F02F 1/00 20060101
F02F001/00 |
Claims
1-5. (canceled)
6. A combustion chamber structure for an internal combustion
engine, comprising: a concave portion that is formed in a piston
top part in an eccentric manner relative to a cylinder center; and
a tapered portion that connects an upper end face of the piston top
part and a side face of the concave portion; wherein the tapered
portion is a portion in which, in a case where two regions in which
a squish area width that is a horizontal distance between an outer
edge portion of the upper end face of the piston top part and an
inner edge portion of the tapered portion is the same are compared,
a center of an outer edge portion of the tapered portion is made
eccentric with respect to the cylinder center so that a width in a
horizontal direction of the tapered portion on a side of a region
in which a swirl flow velocity becomes slow is smaller than a width
in the horizontal direction of the tapered portion on a side of a
region in which the swirl flow velocity becomes fast.
7. The combustion chamber structure for an internal combustion
engine according to claim 6 that is a combustion chamber structure
in which two intake valves having mutually different diameters are
arranged, comprising: two valve recesses having different diameters
that are formed in the piston top part in correspondence with the
two intake valves, respectively; wherein among the two valve
recesses, a valve recess that has a larger diameter is arranged in
a region in which a swirl flow velocity is faster in comparison to
a valve recess that has a smaller diameter.
8. The combustion chamber structure for an internal combustion
engine according to claim 6, wherein an eccentric direction with
respect to the cylinder center of the outer edge portion of the
tapered portion is a direction perpendicular to a line segment
connecting the cylinder center and a center of the concave
portion.
9. A combustion chamber structure for an internal combustion engine
that is a combustion chamber structure in which two intake valves
having mutually different diameters are arranged, comprising: two
valve recesses having different diameters that are formed in the
piston top part in correspondence with the two intake valves,
respectively; a concave portion that is formed in the piston top
part in an eccentric manner relative to a cylinder center; and a
tapered portion that connects an upper end face of the piston top
part and a side face of the concave portion; wherein a tapered
portion volume that is a volume of a space formed between the
tapered portion and a combustion chamber upper wall surface in a
first portion of the piston top part is greater than a tapered
portion volume in a second portion that is nearer than the first
portion to an eccentric direction of the concave portion from a
center of the cylinder; and among the two valve recesses, a valve
recess that has a larger diameter is arranged in a region in which
a swirl flow velocity is faster in comparison to a valve recess
that has a smaller diameter.
Description
TECHNICAL FIELD
[0001] The present invention relates to a combustion chamber
structure for an internal combustion engine.
BACKGROUND ART
[0002] A combustion chamber structure for an internal combustion
engine is known in which a shallow-dish type concave portion is
formed in the top face of a piston, and a conical protrusion is
formed on the bottom face of the concave portion. Further, for
example, in Patent Literature 1 a combustion chamber structure is
disclosed that is arranged so as to be eccentric with respect to a
center axis of a cylinder. In Patent Literature 1, a combustion
chamber is formed so that a diameter thereof decreases in the
upward directions, that is, so that a side face of the combustion
chamber inclines towards the center. Further, a lip portion at an
upper end that continues to the side face of the combustion chamber
is subjected to a rounding process. The lip portion is formed at a
lower position than the upper end face of the piston, and a tapered
face is formed from the lip portion to the upper end face of the
piston.
CITATION LIST
Patent Literature
[0003] Patent Literature 1: Japanese Patent Laid-Open No. 03-210021
[0004] Patent Literature 2: Japanese Utility Model Laid-Open No.
59-157535 [0005] Patent Literature 3: Japanese Patent Laid-Open No.
63-094020 [0006] Patent Literature 4: Japanese Patent Laid-Open No.
2000-220520 [0007] Patent Literature 5: Japanese Patent Laid-Open
No. 09-280052
SUMMARY OF INVENTION
Problem to be Solved by the Invention
[0008] According to the configuration disclosed in Patent
Literature 1, a concave portion that constitutes the combustion
chamber is arranged eccentrically from the cylinder center, and the
tapered portion that is formed from the lip portion is also formed
symmetrically with respect to an outer circumferential portion of
the concave portion. Consequently, differences arise with respect
to the sizes of squish areas in this combustion chamber structure.
When a difference exists in the sizes of the squish areas, excess
fuel is liable to exist in a region in which the squish area is
small and excess air is liable to exist in a region in which the
squish area is large. As a result, a situation can occur in which
the air utilization rate decreases. Further, since an imbalance
arises in the flow inside the cylinder as a result of the imbalance
in the squish areas, and in particular since the gas flow velocity
quickens on the side of the large squish area, the cooling loss is
liable to increase.
[0009] Accordingly, an object of the present invention is to solve
the above described problem and provide a combustion chamber
structure for an internal combustion engine that is improved so
that the air utilization rate can be improved while homogenizing
the gas flow inside a cylinder and reducing cooling loss even in a
case where a concave portion of a combustion chamber is arranged
eccentrically from a cylinder center axis.
Means for Solving the Problem
[0010] To achieve the above described object, the present invention
provides a combustion chamber structure for an internal combustion
engine, comprising: a concave portion that is formed in a piston
top part in an eccentric manner relative to a cylinder center axis;
and a tapered portion that connects an upper end face of the piston
top part and a side face of the concave portion. The tapered
portion is formed so that a tapered portion volume in a first
portion of the piston top part is greater than a tapered portion
volume in a second portion that is nearer than the first portion to
an eccentric direction of the concave portion from the cylinder
center axis. Note that the tapered portion volume is a volume of a
space formed between the tapered portion and a combustion chamber
upper wall surface.
[0011] In the present invention, the tapered portion may be
informed so that a tapered portion depth in the first portion is
greater than a tapered portion depth in the second portion. Note
that the tapered portion depth is a distance from a face of a same
height as the upper end face of the tapered portion.
[0012] In the present invention, the tapered portion may be
informed so that a tapered portion width in the first portion is
greater than a tapered portion width in the second portion. Note
that a tapered portion width is a distance in a planar direction
perpendicular to the cylinder center axis from an outer edge
portion of the tapered portion that is a boundary portion between
the tapered portion and the upper end face to an inner edge portion
of the tapered portion that is a boundary portion between the
tapered portion and the side face of the concave portion.
[0013] In the present invention, the tapered portion may be
informed so that the tapered portion volume in a third portion of
the piston top part is greater than the tapered portion volume in a
fourth portion in which a flow velocity of a swirl flow that flows
into the combustion chamber is slower than in the third
portion.
[0014] The present invention may be applied to a combustion chamber
structure in which two intake valves having mutually different
diameters are arranged. In this case, two valve recesses are
assumed to be formed in the piston top part in correspondence with
the two intake valves, respectively. And, among the two valve
recesses, a region in which a larger valve recess corresponding to
an intake valve having a larger diameter is formed may be a region
in which a flow velocity of a swirl flow becomes faster than in a
region in which a smaller valve recess corresponding to an intake
valve having a smaller diameter is formed.
Advantageous Effects of Invention
[0015] In a case where a cavity that is a concave portion
constituting a combustion chamber that is formed in a piston top
part is arranged eccentrically with respect to a cylinder center
axis, the surface area of a squish area is greater in a region in
an opposite direction to the eccentric direction of the cavity in
comparison to a region that is near to the eccentric direction.
However, in this respect, according to the present invention, in
comparison to a portion that is near (second portion) the eccentric
direction of the cavity, a larger tapered portion volume is secured
at a portion (first portion) that is far from the eccentric
direction, that is, a portion at which the squish area is larger.
Consequently, it is possible to promote leading of the air-fuel
mixture into a large squish area and decrease residual air therein,
and thus the air utilization rate can be improved. Further, the
overall flow of gas can be homogenized and a cooling loss can be
reduced.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a view for describing a constitution of a piston
top face part according to Embodiment 1 of the present
invention.
[0017] FIG. 2 is a view for describing the constitution of the
piston top face part according to Embodiment 1 of the present
invention.
[0018] FIG. 3 is a view for describing a tapered portion depth and
volume of a squish area 30 with respect to a squish area width of
the piston in the present Embodiment 1.
[0019] FIG. 4 is a view for describing a cooling loss with respect
to the amount of NOx emissions in relation to the combustion
chamber structure of Embodiment 1 of the present invention.
[0020] FIG. 5 is a view for describing the amount of smoke emission
with respect to the amount of NOx emission according to the
combustion chamber structure of Embodiment 1 of the present
invention.
[0021] FIG. 6 is a view for describing an example of another shape
of the piston of Embodiment 1 of the present invention.
[0022] FIG. 7 is a view for describing an example of another shape
of the piston of Embodiment 1 of the present invention.
[0023] FIG. 8 is a view for describing a constitution of a piston
top face part according to Embodiment 2 of the present
invention.
[0024] FIG. 9 is a view for describing a constitution of a piston
top face part according to Embodiment 3 of the present
invention.
DESCRIPTION OF EMBODIMENTS
[0025] Embodiments of the present invention are described hereunder
with reference to the accompanying drawings. For each of the
drawings, the same or corresponding portions are denoted by the
same reference numerals, and a description of such portions is
simplified or omitted.
Embodiment 1
[0026] FIG. 1 and FIG. 2 are views for describing a piston
according to Embodiment 1 of the present invention. FIG. 1 is a
view that includes a cylinder center axis C1 of the piston, and
shows a cross-section in a direction parallel to the cylinder
center axis C1. FIG. 2 is a view that shows a top face of a piston
top part as viewed from above (that is, from the upper direction on
the paper surface in FIG. 1). A piston 10 of the present Embodiment
1 is mounted inside each cylinder of a diesel engine and used, and
constitutes a combustion chamber that takes a cylinder head as an
upper wall surface inside each cylinder.
[0027] As shown in FIG. 1, the piston 10 includes a cavity 12 that
is a space constituting a combustion chamber, which is formed in a
concave shape in a top part of the piston 10. A protruding portion
16 that protrudes in a conical shape towards a center portion of
the cavity 12 is provided in a bottom face 14 of the cavity 12. The
bottom face 14 of the cavity 12 continues gradually into a side
face 18 via a curved face 14a. The side face 18 of the cavity 12 is
a wall surface that extends in an upward direction approximately
parallel to the direction of the cylinder center axis C1.
[0028] In the present Embodiment 1, the center axis C1 of the
cylinder is arranged in a state in which the center axis C1
deviates from a center C2 of the cavity 12. In FIG. 1 and FIG. 2,
the center axis C1 of the cylinder is formed eccentrically in the
right direction in the figures. Hereunder, a direction from the
cylinder center axis C1 towards the cavity center C2 (right
direction in the figures) is also referred to as an "eccentric
direction of the cavity 12".
[0029] The side face 18 of the cavity 12 continues into a tapered
portion 20 formed in a top part of the piston 10, via a
round-shaped curved face 20a of the tapered portion 20. The tapered
portion 20 continues into an upper end face 22 of the top part of
the piston 10. That is, the tapered portion 20 including the curved
face 20a is a face that connects the upper end face 22 that is the
upper end face of the piston 10 and the side face 18 of the cavity
12, and is a face that is diagonally formed with respect to a
horizontal plane of the cylinder (that is, a plane perpendicular to
the cylinder center axis C1).
[0030] When the piston 10 is viewed from above as shown in FIG. 2,
a boundary line between the tapered portion 20 and the upper end
face 22, namely, an outer edge portion 20b of the tapered portion
20, is formed so that the center thereof is located at the same
position as the center axis C1 of the cylinder.
[0031] In the following embodiments, a squish area 30 is a
clearance between the top part of the piston 10 and a cylinder head
(not shown in the drawings) that can be formed in an area that is
located further to the outer circumferential side than the cavity
12 when the piston 10 reaches top dead center. That is, according
to the present Embodiment 1, a space between the upper end face 22
and tapered portion 20 and the cylinder head corresponds to the
squish area 30.
[0032] Further, in the following embodiments, the term "depth"
refers to a distance in the cylinder center axis C1 direction, and
the term "width" refers to a distance in the direction of a
horizontal plane that is a plane perpendicular to the cylinder
center axis C1. A tapered portion depth H represents a distance in
the vertical direction to the upper end face 22 from each point on
an inner edge portion 20c of the tapered portion 20 that is a
boundary line between the curved face 20a of the tapered portion 20
and the side face 18. In addition, it is assumed that the term
"squish area width W" refers to a shortest distance in the
horizontal direction between the inner edge portion 20c of the
tapered portion 20 and an outer circumferential circle 22a of the
upper end face 22.
[0033] Hereunder, the configuration of the squish area 30 of the
piston 10 of the present Embodiment 1 is described. FIG. 3 is a
view for describing the tapered portion depth H and the volume of
the squish area 30 with respect to the squish area width W of the
piston 10 in the present Embodiment 1. In FIG. 3, the horizontal
axis represents an angle .theta., the vertical axis represents the
tapered portion depth H or the volume of the squish area 30, a
curve (a) represents the tapered portion depth H, and a curve (b)
represents the volume of the squish area 30. In FIG. 3, the angle
.theta. is an angle in a case where the apex angle is taken as the
cavity center C2 and a line obtained by extending a line segment
connecting the cylinder center axis C1 and the cavity center C2 in
the eccentric direction is assumed to have an angle .theta.=0
degrees.
[0034] Since the cavity 12 is eccentric in a direction in which
.theta.=0 degrees, as shown in FIG. 3, the squish area width W that
is the width of a portion located further on an outer side relative
to the cavity 12 of the top part of the piston 10 reaches a maximum
when .theta.=180 degrees, gradually decreases towards a side on
which .theta.=0 degrees (or 360 degrees), and reaches a minimum
when .theta.=0 degrees (or 360 degrees).
[0035] The outer edge portion 20b of the tapered portion 20 is
formed so as to be concentric with the cylinder center axis C1, and
the cavity 12 is eccentric in a direction in which .theta.=0
degrees with respect to the cylinder center axis C1. Accordingly,
the width of the piston upper end face 22 is uniform overall. On
the other hand, with respect to the width of the tapered portion
20, a horizontal distance between the outer edge portion 20b and
the inner edge portion 20c also reaches a minimum width when
.theta.=0 degrees (or 360 degrees) that is the eccentric direction
thereof, and gradually increases towards the side on which
.theta.=180 degrees in an opposite direction to the eccentric
direction, and reaches a maximum width when .theta.=180
degrees.
[0036] In addition, according to the present Embodiment 1, as shown
by the curve (a) in FIG. 3, the tapered portion depth H is formed
so gradually deepen as the squish area width W increases. That is,
the tapered portion depth H is at a minimum when .theta.=0 degrees
(or 360 degrees), and gradually increases in the direction in which
.theta.=180 degrees, and reaches a maximum depth when .theta.=180
degrees.
[0037] That is, according to the present Embodiment 1, the tapered
portion depth H and the width of the tapered portion 20 are both
formed so as to increase as the width W of the squish area
increases. Therefore, as shown by the curve (b), the volume of the
squish area 30 also increases as the squish area width W increases.
In other words, the width and depth of the tapered portion 20 at a
certain portion (first portion) of the piston top part are larger
than the width and depth of the tapered portion 20 at another
portion (second portion) that is nearer to the eccentric direction
(.theta.=0 degrees) than the certain portion. Accordingly, the
tapered portion volume of the certain portion (first portion) is
greater than the tapered portion volume of the other portion
(second portion), and the squish area volume of the certain portion
(first portion) is greater than the squish area volume of the other
portion (second portion).
[0038] According to the combustion chamber structure of the present
Embodiment 1 that is configured as described above, a larger
tapered portion 20 is provided in the larger squish area 30.
Therefore, the flow velocity of an air-fuel mixture in a large
squish area 30a can be decreased. Accordingly, a heat transfer
coefficient can be lowered and a cooling loss caused by a rise in
the temperature of the piston 10 or the like can be decreased.
[0039] Further, the tapered portion 20 is configured to be deeper
on the large squish area 30a side on which the amount of residual
air is liable to become large. Consequently, it is possible to
promote leading of the air-fuel mixture to the large squish area
30a and thereby improve the air utilization rate.
[0040] FIG. 4 is a view for describing a cooling loss with respect
to the amount of NOx emissions in relation to the combustion
chamber structure of Embodiment 1 of the present invention. In FIG.
4, the horizontal axis represents the amount of NOx emission
(g/kWh) and the vertical axis represents the cooling loss (%). A
line plotted with triangle symbols represents the case of the
combustion chamber structure according to the present Embodiment 1,
and for comparison, a combustion example in the case of the
conventional combustion chamber structure is represented by a line
plotted with circle symbols. From FIG. 4, it is verified that in
comparison to the conventional combustion chamber structure,
cooling loss is significantly decreased when using the combustion
chamber structure of the present Embodiment 1.
[0041] FIG. 5 is a view for describing the amount of smoke emission
with respect to the amount of NOx emission according to the
combustion chamber structure of Embodiment 1 of the present
invention. In FIG. 5, the horizontal axis represents the amount of
NOx emission (g/kwh) and the vertical axis represents the amount of
smoke emission FSN. A line plotted with triangle symbols represents
the case of the combustion chamber structure according to the
present Embodiment 1, and for comparison, a combustion example in
the case of a combustion chamber structure having the conventional
shape is represented by a line plotted with circle symbols. From
FIG. 5, it is verified that in comparison to the conventional
combustion chamber structure, NOx emissions and smoke emissions are
both reduced when using the combustion chamber structure of the
present Embodiment 1.
[0042] Note that, in FIG. 1 and FIG. 2 of the present Embodiment 1
a case is described in which the tapered portion 20 and the side
face 18 are connected by a round-shaped curved face 20a. By
providing the curved face 20a in this manner, a temperature rise at
the edge portion can be effectively suppressed, and improvement of
cooling loss and prevention of deformation and melting loss of the
piston can be achieved. However, the present Embodiment 1 is not
limited thereto, and a configuration may also be adopted in which
the tapered portion 20 and the side face 18 are connected in an
angulated state by a flat surface, and which does not have the
curved face 20a that has been processed in a round shape.
[0043] Further, according to the present Embodiment 1, a case has
been described in which both the width and the depth H of the
tapered portion 20 are configured to increase as the squish area 30
increases and, consequently, the squish area volume also increases
as the squish area width W increases. However, the present
invention is not limited thereto, and for example, a configuration
may also be adopted so that, as the width W of the squish area 30
increases, only the tapered portion depth H deepens and the width
of the tapered portion 20 is uniform or is varied independently of
the squish area width W. Further, a configuration may also be
adopted in which, as the squish area width W increases, only the
width of the tapered portion 20 widens and the tapered portion
depth H is uniform or the depth changes independently of the squish
area width W. Even when such configurations are adopted, as the
squish area width W increases, the volume of the squish area 30 can
be increased and thus the air utilization rate can be improved and
smoke emissions can be reduced. The same also applies to the
embodiments described below.
[0044] Further, according to the present Embodiment 1, a case was
described in which the center of the outer edge portion 20b of the
tapered portion 20 is configured so as to match the cylinder center
axis C1. However, the present invention is not limited thereto, and
a configuration may also be adopted in which the cylinder center
axis C1 and the center of the outer edge portion 20b of the tapered
portion 20 deviate relative to each other. Further, the outer edge
portion 20b of the tapered portion 20 is not limited to an edge
portion that is formed in a circular shape when viewing the top
part of the piston 10 from above, and for example, may be formed in
an elliptical shape. In the case of these configurations also, by
forming the tapered portion 20 so that the width of the tapered
portion 20 and/or the tapered portion depth increase in a region in
which the squish area width W is large, a large volume can be
secured with respect to the squish area 30. As a result, the air
utilization rate can be improved and the amount of smoke emission
can be reduced. The same also applies to the embodiments described
below.
[0045] Furthermore, according to the present Embodiment 1 a case
has been described in which the volume of the squish area 30 is
designed to gradually increase by gradually increasing the tapered
portion depth H and the width of the tapered portion 20 as the
squish area 30 increases. However, according to the present
invention, a change in the volume of the squish area 30 is not
limited thereto, and a configuration may also be adopted in which
the width or depth H of the tapered portion and the volume of the
squish area 30 change in a stepwise manner with respect to each
region. That is, a configuration may be adopted in which the
tapered portion depth H and/or width in a certain region (first
portion) in which the squish area 30 is large is formed to be large
in comparison to the tapered portion depth H and/or width in
another region (second region) in which the squish area 30 is
smaller than in the certain region. The same also applies to the
embodiments described below.
[0046] In addition, according to the present Embodiment 1, a case
has been described in which the squish area volume is designed to
increase in accordance with an increase in the squish area width W
by forming the tapered portion 20 so that the tapered portion depth
H and the width of the tapered portion 20 increase in accordance
with an increase in the squish area width W. However, in the
present invention the configuration of the squish area 30 is not
limited to the aforementioned configuration and, for example, a
configuration may be adopted in which the squish area width W is
made uniform overall.
[0047] FIG. 6 and FIG. 7 are views for describing an example of
another shape of the piston 10 of Embodiment 1 of the present
invention. In the example illustrated in FIG. 6, the tapered
portion 20 is not provided as in FIG. 1, and a side face 118 of a
cavity 112 is directly connected to an upper end face 122 of the
piston 10. According to this example, an angle of the side face 118
of the cavity 112 is changed so that the squish area width W, that
is, the width of the upper end face 122, is the same size
throughout the entire combustion chamber. That is, a configuration
is adopted so that an angle between the side face 118 and the upper
end face 122 becomes a minimum angle a at a certain portion in the
eccentric direction (.theta.=0 degrees or 360 degrees) of the
cavity 112, and the angle gradually increases in accordance with an
increase in distance from the eccentric direction, and on the
opposite side (.theta.=180 degrees) to the eccentric direction, the
angle between the side face 118 and the upper end face 122 becomes
a maximum angle .beta..
[0048] In the example shown in FIG. 7, the conical protruding
portion 216 of the bottom face 214 of the cavity 212 is formed so
as to deviate from the cavity center C2. On the other hand, the
center of a boundary line 212a between the side face 218 of the
cavity 212 and an upper end face 222 is configured so as to match
the cylinder center axis C1 when viewing the cavity 212 from the
upper side. That is, according to the combustion chamber structure
illustrated in FIG. 7, the width between a center C3 of the conical
protruding portion 216 and the side face 218 is a smallest distance
L2 at a certain portion on an extension of the eccentric direction
of the conical protruding portion 216, and gradually lengthens in
accordance with an increase in distance from the eccentric
direction and reaches a largest distance L1 on an opposite side to
the eccentric direction. Thus, the squish area width W is made
uniform throughout the entire combustion chamber.
[0049] By making the size of the squish area equal throughout the
entire combustion chamber as in the configurations illustrated in
FIGS. 6 and 7, it is possible to reduce cooling loss and also
reduce the amount of smoke emission.
[0050] Further, in the examples shown in FIGS. 6 and 7 a
configuration is illustrated in a case where a connecting portion
between the side face 118 and the upper end face 122 or a
connecting portion between the side face 218 and the upper end face
222 is formed in an angulated edge shape. However, the present
invention is not limited thereto, and a connecting portion between
the side face 118 or 218 and the upper end face 122 or 222 may be a
portion that has been processed in a round shape. It is thereby
possible to suppress a rise in temperature at the edge portion even
more effectively to improve the cooling loss and inhibit
deformation or melt loss that is caused by thermal stress of the
piston 10.
Embodiment 2
[0051] FIG. 8 is a view for describing a piston according to
Embodiment 2 of the present invention. The piston illustrated in
FIG. 8 is identical to the piston 10 illustrated in FIG. 1 and FIG.
2 except that the position of a center C4 of an outer edge portion
20a of the tapered portion 20 is different relative to the piston
10 illustrated in FIG. 1 and FIG. 2.
[0052] For example, in the combustion chamber in which the cavity
12 is formed eccentrically as in the combustion chamber
configuration illustrated in FIG. 1 and FIG. 2, it is known that
even in areas in which the squish area volume is the same, that is,
areas that are symmetrical with respect to the eccentric direction,
the velocity of a swirl flow increases in a downstream part of the
swirl flow.
[0053] Therefore, in the present Embodiment 2 also, the center C2
of the cavity 12 is formed eccentrically with respect to the center
C1 of the cylinder. According to this configuration, the squish
area width W is the same at portions that are mutually symmetrical
with respect to the eccentric direction. In addition, according to
the present Embodiment 2, the center C4 of the outer edge portion
20b of the tapered portion 20 is formed so as to be eccentric on
the side of a region in which the swirl flow velocity increases.
Consequently, when regions in which the squish area width W is the
same and that are at symmetrical positions with respect to the
eccentric direction are compared, a width X of the tapered portion
20 on the side of the region in which the swirl flow velocity is
faster (third portion) will be greater than the width X of the
tapered portion 20 on the side of the region in which the swirl
flow velocity is slower (fourth portion).
[0054] More specifically, as shown in FIG. 8, in a case where a
swirl flow arises from the lower part, the center C4 of the outer
edge portion of the tapered portion 20 is made eccentric from the
cylinder center axis C1 in a vertically upward direction (direction
in which .theta.=90 degrees) with respect to a line segment (line
segment of .theta.=0 degrees) that connects the center axis C1 and
the cavity center C2. As a result, when the portions that have the
same squish area width are compared, the width of the tapered
portion 20 is larger in the portion in which the swirl flow
velocity increases (third portion). Therefore, a larger squish area
volume can be secured in the region in which the swirl flow
velocity increases.
[0055] The flow of gas inside the cylinder can be homogenized by
securing a large squish area volume in the flow velocity direction
in this manner. It is thereby possible to improve the mixed state
of the air-fuel mixture and improve the cooling loss.
[0056] Note that according to the present Embodiment 2 a case has
been described in which the center C4 of the outer edge portion 20b
of the tapered portion 20 is made eccentric from the cylinder
center axis C1 in a direction in which .theta.=90 degrees. However,
the present invention is not limited thereto, and it is sufficient
to adopt a configuration in which the tapered portion 20 is caused
to deviate so that when portions that have the same squish area
width W are compared, the width X of the tapered portion 20 on the
side of a portion at which the swirl flow velocity increases is
wider.
[0057] Further, a change with respect to the width X of the tapered
portion 20 in the present invention is not limited to one in which
the width X gradually changes in the direction of the swirl flow
velocity, as described in the above Embodiment 1. For example, a
configuration may also be adopted so that in a case where two or
more regions with respect to which a large difference is liable to
arise in the swirl flow velocity are identified and tapered
portions having the same squish area widths are compared between
such regions, the widths of the tapered portions are varied in a
stepwise manner so that the width of a tapered portion within a
region in which the swirl flow velocity is faster is wider. The
same also applies to the embodiment described below.
[0058] In addition, according to the present Embodiment 2, a case
has been described in which, by varying the width of the tapered
portion 20, the squish area volume of a region in which the swirl
flow velocity is faster is made relatively larger. However, the
present invention is not limited thereto, and a configuration may
also be adopted in which the tapered portion depth is varied
gradually or in a stepwise manner so that, when regions having the
same squish area width are compared, the tapered portion depth H is
deeper in a region in which the swirl flow velocity is faster.
Furthermore, the present invention may be a configuration obtained
by combining the foregoing configurations or in which both the
width of the tapered portion 20 and the tapered portion depth are
varied. The same also applies to the embodiment described
below.
Embodiment 3
[0059] FIG. 9 is a view that illustrates a piston according to
Embodiment 3 of the present invention. The piston 10 illustrated in
FIG. 9 is used in cylinders in which two intake valves are
provided, respectively, in which the diameters of the intake valves
are different. The piston 10 shown in FIG. 9 is identical to the
piston 10 shown in FIG. 1 and FIG. 2 except that, in the top face
thereof, valve recesses 40 are formed that correspond to the intake
valves of differing diameters, and that the position of the center
C4 of the outer edge portion 20a of the tapered portion 20 is
shifted relative to the piston 10 shown in FIG. 1 and FIG. 2.
[0060] In this case the valve recesses are hollows in the piston
top part that are provided to prevent the occurrence of
interference between the intake valves and the piston top part when
the intake valves open. According to the combustion chamber of the
present Embodiment 3, it is assumed that a swirl flow arises in the
arrow direction from the lower part to the upper part on the paper
surface. As described above, the flow velocity on the downstream
side of the swirl flow increases in comparison to the flow velocity
on the upstream side of the swirl flow. In this case, an intake
valve having a small diameter is installed on the upstream side of
the swirl flow, and an intake valve having a large diameter is
installed on the downstream side of the swirl flow.
[0061] As shown in FIG. 9, in the piston top part, a small recess
40a that corresponds to the intake valve that has the small
diameter is formed on the upstream side of the swirl flow. Further,
a large recess 40b that is larger than the small recess 40a and
that corresponds to the intake valve that has the large diameter is
formed on the downstream side of the swirl flow. By providing the
large recess 40b on the downstream side of the swirl flow in this
manner, the flow of the air-fuel mixture can be attenuated on the
large recess 40b side and the flow of gas inside the cylinder can
be homogenized.
[0062] In addition, according to the present Embodiment 3,
similarly to Embodiment 2, the center C4 of the outer edge portion
20b of the tapered portion 20 is made eccentric on the side of the
large recess 40b that is the downstream side of the swirl flow.
More specifically, the tapered portion 20 is formed so that the
center C4 of the outer edge portion 20b of the tapered portion 20
is located at an eccentric position relative to the cylinder center
axis C1 in a vertically upward direction (direction in which
.theta.=90 degrees) with respect to a line segment connecting the
cylinder center axis C1 and the cavity center C2. Thus, when
comparing the regions having the same squish area width, the width
of the tapered portion 20 is greater on the side on which the large
recess 40b is provided, and a larger squish area volume can be
secured on that side. Therefore, the amount of residual air can be
reduced on the side of the large recess 40b and the air utilization
rate can be improved.
[0063] In Embodiment 3 that has been described above, a case is
described in which the outer edge portion a of the tapered portion
20 is made eccentric on the side of the large recess 40b, and the
volume of the squish area 30 is larger on the large recess 40b
side. However, the present invention is not limited thereto, and a
configuration may also be adopted in which the center of the outer
edge portion 20b is not made eccentric on the large recess 40b
side. That is, a configuration may also be adopted so that, when
regions having the same squish area width W are compared, excluding
a difference in volume that corresponds to the amount of the hollow
for the valve recesses, the same volume of the squish area 30 is
secured on the large recess 40b side and the small recess 40a
side.
[0064] Further, according to the present Embodiment 3, similarly to
Embodiment 2, a case has been described in which the width of the
tapered portion 20 is gradually changed by shifting the center C4
of the outer edge portion 20b in a direction perpendicular to the
eccentric direction. However, the present invention is not limited
thereto, and it is sufficient to adopt a configuration in which the
squish area volume is changed gradually or in a stepwise manner so
that when portions that have the same squish area width of the
region formed by the large recess 40b and the region formed by the
small recess 40a are compared, the squish area volume on the large
recess 40b side is greater than the squish area volume on the small
recess 40b side.
[0065] It is to be understood that even when the number, quantity,
amount, range or other numerical attribute of an element is
mentioned in the above description of the embodiments, the present
invention is not limited to the mentioned numerical attribute
unless it is expressly stated or theoretically defined. Further,
structures and the like described in conjunction with the
embodiments are not necessarily essential to the present invention
unless expressly stated or theoretically defined.
DESCRIPTION OF REFERENCE NUMERALS
[0066] 10 Piston [0067] 12 Cavity (concave portion) [0068] 14
Bottom face [0069] 14a Curved face [0070] 16 Protruding portion
[0071] 18 Side face [0072] 20 Tapered portion [0073] 20a Curved
face of tapered portion [0074] 20b Outer edge portion of tapered
portion [0075] 20c Inner edge portion of tapered portion [0076] 22
Upper end face [0077] 22a Outer circumferential circle [0078] 30
Squish area [0079] 112, 212 Cavity [0080] 212a Boundary line [0081]
214 Bottom face [0082] 216 Protruding portion [0083] 118, 218 Side
face [0084] 122, 222 Upper end face [0085] 230 Squish area [0086]
40a Small recess [0087] 40b Large recess [0088] C1 Cylinder center
axis [0089] C2 Cavity center [0090] C3 Protruding portion center
[0091] C4 Outer edge portion center
* * * * *